PROJECT SUMMARY The transition from childhood via puberty to early adulthood is a developmental period that may influence future health and disease. In women, data on duration and timing from menarche to the establishment of normal reproductive activity is sparse. In boys, limited data are available on their pubertal development. Understanding normal trajectories of pubertal transitions for boys and girls throughout adolescence will facilitate earlier diagnosis of atypical pubertal development. Improved methods and further investigations are necessary to characterize this transition and its consequences. Several studies suggest that prenatal exposures are linked to ages of onset of various pubertal events; although mechanisms are unknown. Recently, epigenetic marks such as the addition of methyl groups at cytosine-phosphate-guanine sites (CpGs) have been suggested to explain the link of prenatal conditions to age of onset of puberty events. The fetus is considered to adapt to prenatal conditions by changing its epigenetic make-up leading to differentially methylated CpG sites, which are semi-stable epigenetic memories of exposures. However, it is not known yet which specific CpGs are associated with ages of onset of pubertal events. To improve our mechanistic understanding the proposed secondary analysis of existing data will address two aims. In Specific Aim 1 (SA1), we will use whole epigenome DNA methylation (DNA-M) from 864 Guthrie cards data collected at birth to predict ages of onset of pubertal events (439 boys and 425 girls). In SA2, we will identify post-pubertal DNA-M changes. To this end we will analyze existing DNA-M data collected at age 10 and 18 years (400 pairs of boys and girls at each age) to determine whether the age of attaining puberty is related to DNA-M at 18 years or to change in DNA-M (?DNA-M) from 10 to 18 years. Our research team has a long track record of successful collaboration linking epidemiological data on pubertal development by applying biostatistical methods and epigenetic expertise. The proposal is of high importance since it has the potential to change the way pubertal transitions can be managed in the future by being proactive at birth and during childhood, rather than waiting for the individuals to develop reproductive problems and symptoms later in life.